This invention relates to a device and a method for the sustained release of a substance. In one embodiment, this invention relates to a bolus which is administered orally to a ruminant and which dispenses controlled amounts of a therapeutic, additive or nutrient substance over a prolonged period of time into the reticulorumen of the ruminant.
It is well known that ruminant animals, such as beef cattle and sheep, are able to digest large quantities of low quality feeds. These feeds, comprising mostly cellulose are swallowed with little chewing. They are ingested into the largest of four stomachs, called the rumen. The rumen is not a true stomach inasmuch as it contains no digestive glands. It is more in the nature of a storage compartment, a mixing organ, and a reservoir containing a large concentration of bacteria. The bacteria in the rumen break up the complex cellulose components of the feed into simpler substances which are more readily digested. The feed is then regurgitated by the animal, masticated into finer particles, and reswallowed. When the particles are reduced to a certain critical size, they pass out of the rumen for further digestion in the true stomach.
The cattle industry has long sought devices which release therapeutic, additive or nutrient substances into the rumen in a controlled fashion over an extended period of time. The recent development of high quality feed additives, such as the feed additive Rumensin.RTM. (a trademark of Eli Lilly and Company), has increased the need for such devices. These feed additives improve feed efficiency and promote growth of the cattle. However, the additives must be given orally and must be consumed in small quantities at frequent and regular intervals. These requirements make it difficult to administer the feed additives properly.
Most beef cows and growing calves are allowed to graze over a wide area of pasture land. Thus, it is highly inconvenient for cattle ranchers to administer a dosage of the feed additives daily. Furthermore, many cattle ranchers are also farmers and are unable to devote the time necessary to administer the feed additives. No system or device has yet been disclosed by which these feed additives can be satisfactorily and inexpensively dispensed in the manner required to grazing ruminants.
Several sustained release delivery systems are disclosed in the prior art. U.S. Pat. No. 3,056,724 (Marston) discloses therapeutic pellets for ruminants. These pellets rely upon their size and density to remain inside the rumen, and upon their chemical composition for gradual dissipation of the active agent. U.S. Pat. No. 3,844,285 (Laby) discloses an expandible device for administration to ruminants. The device has a body portion comprising or containing an effective amount of an active agent. Sustained release is achieved by incorporating or coating the active agent with materials having low solubility or permeability in rumen liquor. The device, in a compressed configuration, is given orally to the ruminant. After entering the rumen, the device assumes an expanded configuration and is thereby retained within the rumen.
Other patents, such as U.S. Pat. Nos. 3,608,549 (Merrill), 4,135,514 (Zaffaroni et al.), 4,180,558 (Goldberg et al.), and 4,207,890 (Mamajek et al.), disclose devices for the sustained release of drugs to warm blooded animals, especially humans. These devices depend upon an unpredictable rate of release. None of the devices described in these patents is particularly suitable for the prolonged administration of feed additives in the quantity required to ruminants in a predictable controlled manner.
Thus, there remains a need for a simple and inexpensive device to release a substance in measured amounts over a prolonged period of time.
There is also a need for a device of this kind which is particularly suitable for the administration of therapeutic, additive or nutrient substances into the reticulorumen of ruminants.
There is also a need for a device of this kind which meets the needs of the cattle industry.